1. Field of the Invention
The present invention relates to a photographing apparatus, a photographing method and a computer readable storage medium storing a program therein.
2. Related Art
Heretofore, a photographing apparatus such as a digital camera or the like is known. The photographing apparatus has a continuous shooting function for continuously (serially) shooting a subject that moves (a moving subject) and generating a plurality of pieces of photographed image data of the subject.
Moreover, an image combining apparatus is known, wherein the image combining apparatus combines a plurality of pieces of image data generated by continuously shooting the moving subject by a photographing apparatus, and generates image data (moving subject continuous shoot combined image data) indicating a motion of the moving subject by a single image (see, for example, Japanese Patent Application Laid-Open Publication No. 2006-5452).
Moreover, in a field of a photographing apparatus having an interval photographing function for photographing images at a predetermined time interval to take movies for monitoring or the like, a photographing apparatus that automatically changes a setting of serial shoot duration to be shortened by determining that there is a change when a difference between photographed images (change of brightness, motion of the moving subject or the like) is larger than a set value (threshold value), is suggested (see, for example, Japanese Patent Application Laid-Open Publication No. 2002-218309).
However, in the traditional image combining apparatus, the motion of the moving subject, which enters the frame, moves around the frame and leaves from the frame, would have to be shot continuously within a restricted maximum burst for continuous shooting. For example, in a case of taking photographs of the moving subject that passes through the frame in one sec, with the maximum number of images to be shot being set to be twenty, the moving subject can be photographed until the moving subject leaves from the frame, if the continuous shooting starts just after the time when the moving subject enters the frame, and if a continuous shooting speed is set to be equal to or less than 20 fps (frame per second). However, if the moving subject is photographed by the photographing apparatus at a short serial shoot duration, that is the continuous shooting speed is set to be equal to or more than 20 fps, the continuous shooting finishes before the moving subject is out of the frame because of the maximum number of images to be shot.
Similarly, in a case of taking photographs of the moving subject that passes through the frame in two sec, serial shoot duration needs to be set so that a continuous shooting speed is set to be equal to or less than 10 fps, and in a case of taking photographs of the moving subject that passes through the frame in four sec, serial shoot duration needs to be set so that a continuous shooting speed is set to be equal to or less than 5 fps.
FIG. 15A shows an example of moving subject continuous shoot combined image in a case that the continuous shooting speed is set to be larger for a passing speed of the moving subject. FIG. 15B shows an example of moving subject continuous shoot combined image in a case that the continuous shooting speed is set to be smaller for a passing speed of the moving subject. As shown in FIG. 15A, if a photographing is performed at continuous shooting speed fps set to be larger for a passing speed of the moving subject, the moving subject continuous shoot combined image might be the one in which the moving subjects are gathered in a certain area in an angle of view.
Moreover, it cannot be said that an ideal moving subject continuous shoot combined image can be created by merely performing the continuous shooting while a movement of the moving subject from entering the frame to leaving from the frame. For example, if a moving subject passing through the frame in 0.5 sec is photographed at continuous shooting speed of 5 fps, the moving subject can be photographed throughout the frame. However, the number of frames each including the moving subject may be two or so. In this case, as shown in FIG. 15B, the moving subject continuous shoot combined image might be the one in which the number of the moving subject is smaller for the angle of view. The images as shown in FIGS. 15A and 15B are undesirable as the moving subject continuous shoot combined image.
FIG. 16 shows an ideal moving subject continuous shoot combined image. Generally, the ideal moving subject continuous shoot combined image should be considered as such an image that the moving subjects are evenly located in the combined image frame with the moving subjects not significantly being overlapped. The image as shown in FIG. 16 is the ideal moving subject continuous shoot combined image.
Here, a continuous shooting speed that is most preferable for obtaining the ideal moving subject continuous shoot combined image will be explained. Given that the photographing could be performed at such an ideal shutter timing that the first image is shot at the exact moment when the moving subject enters the frame, the maximum number of images to be shot is twenty and the number of frames to be used to be combined is five. In this case, for example, if the moving subject passes through the frame in a quarter sec, then the ideal moving subject continuous shoot combined image can be created most efficiently by continuously shooting five frames at a continuous shooting speed of 20 fps. Moreover, similar images can be created by continuously shooting ten frames at a continuous shooting speed of 40 fps and picking up every second frames from the shot ten frames. The images can also be said as the ideal images.
On the basis of the above, the relationship between a velocity of the moving subject and the continuous shooting speed (fps) for obtaining a moving subject continuous shoot combined image is shown in the next table 1.
TABLE 14020105fpsfpsfpsfpsMoving subject passing through a 5---single frame in ⅛ secMoving subject passing through a10 5--single frame in ¼ secMoving subject passing through a2010 5-single frame in ½ secMoving subject passing through a--2010 5single frame in 1 secMoving subject passing through a----2010single frame in 2 secMoving subject passing through a------20single frame in 4 sec[-] impossible to shoot five frames[--] over the maximum number of images to be shot
As shown in table 1, a plurality of setting values of the fps capable of obtaining the ideal moving subject continuous shoot combined image exist corresponding to passing speeds of the moving subject. However, the ideal moving subject continuous shoot combined images cannot be obtained in the case that the photographing is performed at improper fps. Therefore, a user who photographs for obtaining the moving subject continuous shoot combined image has to predict and set proper value of continuous shooting speed (fps) considering the passing speed of the moving subject and an angle of view before the photographing so as to perform continuous shooting.
Moreover, even if a photographing apparatus is configured to speedup the continuous shooting speed when the moving subject enters the frame as described in Japanese Patent Application Laid-Open Publication No. 2002-218309, the continuous shooting speed at a time when the moving subject enters the frame is constant. Consequently, a continuous shooting speed at a time of combining images may possibly be not an appropriate value.